Conductive film and semiconductor device

ABSTRACT

A conductive film of an embodiment includes: a fine catalytic metal particle as a junction and a graphene extending in a network form from the junction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 13/768,567 filed Feb. 15, 2013,and claims the benefit of priority under 35 U.S.C. §119 from JapanesePatent Applications No. 2012-070004 filed Mar. 26, 2012; the entirecontents of each of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a conductive film and asemiconductor device.

BACKGROUND

A graphene is a two-dimensional nanomaterial composed of carbon atoms.This material has remarkably excellent properties such as a highcurrent-density resistance, an ultrahigh mobility, a high heatresistance, and a high mechanical strength, and therefore has beenregarded as a promising wiring material for a semiconductor devicesimilarly to a carbon nanotube. For example, a graphene nanoribbonshaped into a width of about 10 nm is theoretically expected to have anelectrical conductivity higher than that of copper. Under thecircumstance, studies have been made on the use of the graphene inwirings. A single-layered graphene sheet cannot have a low resistancesimilar to that of a metal, and a multi-layered graphene sheet with alarge area has to be produced at a low temperature to realize the lowresistance.

Currently, the multi-layered graphene sheet with a large area isgenerally produced by growing the graphene on a thin film of a catalyticmetal such as Ni, Fe, or Co at a high temperature of 800° C. or higherin a CVD process. From the viewpoint of suitability for semiconductorprocesses, the catalytic metal is desirably Ni or Co, and the growthtemperature is desirably 600° C. or lower.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view of a semiconductor device according toEmbodiment 1;

FIG. 2 is a conceptual view of a semiconductor device according toEmbodiment 2;

FIG. 3 is a conceptual view of a process for producing the semiconductordevice of Embodiment 2;

FIG. 4 is a conceptual view of a process for producing the semiconductordevice of Embodiment 2;

FIG. 5 is a conceptual view of a process for producing the semiconductordevice of Embodiment 2;

FIG. 6 is a conceptual view of a process for producing the semiconductordevice of Embodiment 2;

FIG. 7 is a conceptual view of a process for producing the semiconductordevice of Embodiment 2;

FIG. 8 is a conceptual view of a process for producing the semiconductordevice of Embodiment 2;

FIG. 9 is a conceptual view of a semiconductor device according toEmbodiment 3;

FIG. 10 is a secondary electron image of a conductive film according toEmbodiment 3;

FIG. 11 is a reflection electron image of the conductive film ofEmbodiment 3;

FIG. 12 is a conceptual view of a semiconductor device according toEmbodiment 4; and

FIG. 13 is a conceptual view of a semiconductor device according toEmbodiment 5.

DETAILED DESCRIPTION

A conductive film of an embodiment includes: a fine catalytic metalparticle as a junction and a graphene extending in a network form fromthe junction.

A semiconductor device of an embodiment includes: a substrate, aninsulation film disposed on the substrate, and a conductive filmdisposed on the insulation film, wherein the conductive film contains afine catalytic metal particle as a junction and a graphene extending ina network form from the junction, and the graphene in the conductivefilm is separated from the insulation film by a gap.

Embodiments will be described below with reference to the drawings.

The conductive film of the embodiment contains the fine catalytic metalparticle as the junction, and the graphene extends therefrom in thenetwork form. The graphene may be formed between the fine catalyticmetal particles.

The conductive film of the embodiment has a two- or three-dimensionalconductive network. The graphene can extend in various directions fromthe starting point of the fine catalytic metal particle M. Therefore,the conductive film can be used not only as a transverse wiring on aplane surface, but also as a via wiring extending in a verticaldirection (between layers) or as a three-dimensional wiring containingan integrated combination of the transverse and vertical wirings.

The conductive film of the embodiment may further contain anothergraphene layer free from the fine catalytic metal particle M.

Embodiment 1

FIG. 1 is a conceptual cross-sectional view of a semiconductor device 10having a conductive film according to Embodiment 1. The semiconductordevice 10 contains a semiconductor substrate 11, an insulation film 12disposed on the semiconductor substrate 11, bonding portions 14 embeddedin a surface of the insulation film 12, catalytic metal portions 13disposed on the bonding portions 14, fine catalytic metal particles 15disposed on the insulation film 12, graphenes 16A disposed between thefine catalytic metal particles 15 or between the fine catalytic metalparticle 15 and the catalytic metal portion 13, and graphenes 16Bstacked over the graphenes 16A. The semiconductor device 10 may furthercontains, in addition to the graphenes 16A and 16B, another graphene orthe like formed between the catalytic metal portions 14 keeping awayfrom the fine catalytic metal particles 15. In FIG. 1, among twocomponents symmetrically arranged, only one component is marked with areference sign. Furthermore, only one graphene is marked with thereference sign 16A, and only one graphene is marked with the referencesign 16B. All the graphenes represented by solid lines between the finecatalytic metal particles 15 or between the fine catalytic metalparticle 15 and the catalytic metal portion 13 correspond to thegraphenes 16A, and all the graphenes represented by solid lines betweenthe catalytic metal portions 13 correspond to the graphenes 16B.

In Embodiment 1, the conductive film contains the graphenes 16A incombination with the fine catalytic metal particles 15, and furthercontains the graphenes 16B stacked over the graphenes 16A. The graphenes16B are formed also above the catalytic metal portions 13. Theconductive film is electrically connected to the catalytic metalportions 13.

In FIG. 1, in a region A surrounded by a dashed line, a gap is formedbetween the insulation film 12 and the graphene 16A. In general, when agraphene is in contact with an insulation film, the graphene interactswith an atom in a main component (such as SiO₂) of the insulation film,whereby an essential property of the graphene is deteriorated. InEmbodiment 1, the graphene 16A is hardly affected by the insulation film12 due to the gap of the region A. This is because the graphene 16A isconnected to the fine catalytic metal particle 15 and thereby may beseparated from the insulation film 12.

In FIG. 1, in a region B surrounded by a dashed line, the graphene 16Ais affected by the fine catalytic metal particle 15. Meanwhile, in aregion C surrounded by a dashed line, the graphene 16A is not affectedby the fine catalytic metal particle 15. In the region B, the graphene16A is affected by the fine catalytic metal particle 15 connectedthereto, whereby an essential property of the graphene 16A isdeteriorated. However, unlike a usual graphene formed on a Cu film orthe like, not all the parts of the graphene 16A are in contact with themetal. Thus, in the region C and the like, though the graphene 16A isthe closest to the insulation film 12, the graphene 16A can be preventedfrom being affected by the metal and the insulation film 12. In theregion C, the graphene 16A can advantageously exhibit the essentialgraphene properties.

In FIG. 1, in a region D surrounded by a dashed line, the graphenes 16Aand 16B are above the fine catalytic metal particle 15, not in contactwith the fine catalytic metal particles 15. Some of the graphenes 16Abetween the fine catalytic metal particles 15 are formed above one finecatalytic metal particle 15, and therefore can be prevented from beingaffected by the fine catalytic metal particle 15 and the insulation film12.

Thus, in FIG. 1, the graphenes 16A and 16B are hardly affected by theinsulation film 12 and the fine catalytic metal particles 15 in theregions other than the region B. Because only a small percentage of thegraphenes 16A is contained in the region B, the graphenes 16A can bemostly prevented from being adversely affected by the external factors.

In Embodiment 1, the semiconductor substrate 11 is a substrate having asemiconducting function. The semiconductor substrate 11 may be a devicesubstrate such as a transistor or a diode, a multi-layered semiconductorstructure such as an LSI, or a photoelectric conversion device such as asolar cell.

In Embodiment 1, the insulation film 12 is a film having an insulationproperty such as a silicon oxide film.

In Embodiment 1, the catalytic metal portion 13 may contain a catalyticmetal such as a metal selected from Cu, Ni, Co, Fe, Ru, Ti, In, Pt andthe like, an alloy containing two or more metals selected from the groupincluding the above metals, or an alloy composed of two or more metalsselected from the group including the above metals. Though the catalyticmetal portion 13 has a vertical surface in FIG. 1, the surface may bepartially or entirely inclined. The total number of the graphenesdepends on the thickness of the catalytic metal portion 13. For example,the catalytic metal portion 13 has a thickness of 10 to 50 nm. In a casewhere the graphenes are grown not at a high temperature of 800° C. orhigher but at a low temperature of 300° C. to 700° C., the catalyticmetal portion 13 preferably contains Ni or Co. Furthermore, in such alow-temperature process, the catalytic metal portion 13 preferably has afacet, which often acts as a starting point for the graphene growth. Thefacet of this embodiment includes an {nn0} or {n00} surface of thecatalytic metal, and has a surface length of 1 to 50 nm. The {nn0} or{n00} surface readily acts as a starting point for the graphene growth.

In Embodiment 1, the bonding portion 14 is a member excellent in bondingto both of the insulation film 12 and the catalytic metal portion 13.Specific examples of materials for the bonding portion 14 include Ti,TiN, and TaN. The catalytic metal portion 13 is often poor in bonding tothe insulation film 12. When the catalytic metal portion 13 is formeddirectly on the insulation film 12, the catalytic metal portion 13 isoften readily peeled off from the insulation film 12. In view ofpreventing the peeling, the bonding portion 14 is preferably placedbetween the insulation film 12 and the catalytic metal portion 13. In acase where the conductive film is used after separated from theinsulation film 12, it is preferred that the bonding portion 14 is notformed.

In Embodiment 1, the fine catalytic metal particles 15 are prepared froma thin film of the above-mentioned catalytic metal deposited on theinsulation film 12, and are dispersed on the insulation film 12. Thethin film of the catalytic metal has a thickness of 1 to 5 nm. The finecatalytic metal particles 15 have a particle diameter of 1 to 100 nm.

Embodiment 2

As shown in the conceptual view of FIG. 2, a semiconductor device 20according to Embodiment 2 contains a semiconductor substrate 21, aninsulation film 22 disposed on the semiconductor substrate 21, bondingportions 24 embedded in a surface of the insulation film 22, catalyticmetal portions 23 disposed on the bonding portions 24, fine catalyticmetal particles 25 disposed on the insulation film 22, graphenes 26Adisposed between the fine catalytic metal particles 25 or between thefine catalytic metal particle 25 and the catalytic metal portion 23, andgraphenes 26B stacked over the graphenes 26A. The semiconductor device20 of Embodiment 2 is the same as the semiconductor device 10 ofEmbodiment 1 except that the catalytic metal portions 23 each have afacet surface 23A.

A method for producing the semiconductor device 20 of Embodiment 2 willbe described below with reference to the conceptual process views ofFIGS. 3 to 8. The processes of FIGS. 3 to 6 may be carried out usingcommon technologies for a known semiconductor device or the like. Asshown in the conceptual process view of FIG. 3, the insulation film 22is formed on the semiconductor substrate 21. As shown in the conceptualprocess view of FIG. 4, a mask 27 for forming the bonding portions 24 isplaced on the components of FIG. 3. As shown in the conceptual processview of FIG. 5, in the insulation film 22 in the components of FIG. 4,regions exposed from the mask 27 are partially removed using alithographic technique. As shown in the conceptual process view of FIG.6, the bonding portions 24 are deposited on the components of FIG. 5.Thus, the bonding portions 24 are embedded in the removed regions of theinsulation film 22. After the embedding of the bonding portions 24, themask 27 is removed.

As shown in the conceptual process view of FIG. 7, a catalytic metalfilm 23 having a nano-scale thickness is deposited on the components ofFIG. 6 using a CVD process or the like. The conditions for forming thecatalytic metal film 23 are preferably selected to control the thicknessof the catalytic metal film 23 as follows. The bonding portions 24 areexcellent in reactivity with a material gas containing a component metalfor the catalytic metal film 23, and the catalytic metal film 23 isreadily deposited on the bonding portions 24. The catalytic metal film23 has a thickness of 10 to 50 nm on the bonding portions 24. Meanwhile,in regions not covered with the bonding portions 24, the catalytic metalfilm 23 is deposited on the insulation film 22. The insulation film 22is poor in the reactivity with the material gas containing the componentmetal for the catalytic metal film 23, and the catalytic metal film 28is not readily deposited on the insulation film 22. Therefore, thecatalytic metal film 23 has a thickness of 1 nm or more but less than 5nm on the insulation film 22. In a case where the bonding portions 24are not formed in the semiconductor device 20, the film formingconditions may be varied to obtain the catalytic metal film 23 havingvarious thicknesses. The facet surface 23A may be formed by a heatingtreatment in an atmosphere such as an H₂, Ar, or N₂ gas atmosphere, aplasma pretreatment using the gas, or the like. The facet surface 23Apreferably has an angle of approximately 35° to 55°. The plane of thecatalytic metal film 23 may be oriented to a {111} surface to form thefacet surface 23A more easily. The amount of the fine catalytic metalparticles 25 on the insulation film 22 can be controlled by changing thethickness of the catalytic metal film 23 on the insulation film 22.

As shown in the conceptual process view of FIG. 8, the components ofFIG. 7 are subjected to a plasma pretreatment, whereby the catalyticmetal film 23 on the insulation film 22 is converted to the fineparticles. The plasma pretreatment for the microparticulation is carriedout using a gas of H₂, Ar, N₂, or the like for a treatment time of 30 to300 seconds at a treatment temperature of 25° C. to 300° C. Thistreatment may be carried out once using the gas or twice or more usingthe different gases.

After the microparticulation, the resultant components is subjected to alow-temperature ultrathin carbon film growth treatment and a carbongrowth treatment using a plasma CVD process, so that the semiconductordevice 20 of FIG. 2 is produced. It is not necessary to perform both ofthe low-temperature ultrathin carbon film growth treatment and thecarbon growth treatment. Only one of the treatments may be performed.The low-temperature ultrathin carbon film growth treatment is carriedout using a plasma containing a carbon-based gas such as a methane gasat a temperature of 200° C. to 400° C. for a short time of approximately30 seconds. The carbon growth treatment is carried out using a plasmacontaining a carbon-based gas such as a methane gas at a temperature of300° C. to 700° C. It is preferred that a remote plasma is used toobtain a graphene layer with a high quality.

Embodiment 3

FIG. 9 is a conceptual view of a semiconductor device 30 according toEmbodiment 3. The semiconductor device 30 is intended to be used as amulti-layered structure device such as an LSI. The semiconductor device30 contains a semiconductor substrate 31, an insulation film 32 disposedon the semiconductor substrate 31, a via hole 32A extending through theinsulation film 32, bonding portion 34A embedded in a bottom of the viahole 32A, bonding portions 34B embedded in a surface of the insulationfilm 32, catalytic metal portions 33A and 33B disposed on the bondingportions 34A and 34B, fine catalytic metal particles 35 disposed on theinsulation film 32, graphenes 36A disposed between the fine catalyticmetal particles 35, between the fine catalytic metal particle 35 and thecatalytic metal portion 33A, or between the fine catalytic metalparticle 35 and the catalytic metal portion 33B, and graphenes 36Bstacked over the graphenes 36A.

SEM images of a conductive film in the semiconductor device 30 of FIG. 9are shown in FIGS. 10 and 11. FIG. 10 is a secondary electron image at25,000-fold magnification. The conductive film is partially peeled offto easily observe the film in the via hole. The conductive film portionin the bottom of the via hole is removed by the peeling and thus cannotbe observed. As is clear from FIG. 10, the conductive film continuouslyextends on the flat surface and the via hole. FIG. 11 is a reflectionelectron image of a region surrounded by a dashed line of FIG. 10 at80,000-fold magnification. In the reflection electron image, brightportions correspond to the fine catalytic metal particles (Ni particles)with a large atomic weight. The carbons (graphene layers) with a smallatomic weight have a dark color approximately equal to that of thebackground, and therefore cannot be discriminated. As is clear fromFIGS. 10 and 11, the fine catalytic metal particles having differentparticle diameters are dispersed in the conductive film, and aconductive network is formed by the combination of the particles and thegraphenes.

In Embodiment 3, a micropore or via wiring and a flat surface wiring canbe grown in a seamless manner in the conductive film. In general, in acase where a carbon nanotube is grown in a vertical direction and agraphene is grown in a transverse direction, another conductivecomponent is required for connecting the carbon nanotube and thegraphene. In contrast, in Embodiment 3, the three-dimensional conductivegraphene network can be formed only by growing the graphenes from thejunctions (starting points) of the fine catalytic metal particles 35.Thus, the graphene wiring can be extended in desired vertical andtransverse directions. The graphenes tend to grow along a wall surface.Therefore, only by forming the fine catalytic metal particles on a wallsurface with a desired shape, the seamless graphene wiring can be formedalong the wall surface.

Embodiment 4

FIG. 12 is a conceptual view of a semiconductor device 40 according toEmbodiment 4. The semiconductor device 40 is intended to be used as atransistor device. The semiconductor device 40 contains atransistor-functional substrate 41, an insulation film 42 disposed onthe substrate 41, bonding portions 44 embedded in a surface of theinsulation film 42, catalytic metal portions 43 disposed on the bondingportions 44, fine catalytic metal particles 45 disposed on theinsulation film 42, graphenes 46A disposed between the fine catalyticmetal particles 45 or between the fine catalytic metal particle 45 andthe catalytic metal portion 43, a gate insulation film 49A disposed onthe graphenes 46A, and a gate electrode 49B disposed on the gateinsulation film 49A. When the graphenes are used as a channel region forcarrying a current in a transistor, the transistor in Embodiment 4 canadvantageously exhibit a high mobility. This is because the graphenesare not in contact with the insulation film 42.

Embodiment 5

FIG. 13 is a conceptual view of a semiconductor device 50 according toEmbodiment 5. The semiconductor device 50 is intended to be used as aphotoelectric conversion device. The semiconductor device 50 contains,for example, a photoelectric conversion layer 51 containing a bufferlayer, a light absorption layer, an electrode, and a support substrate,a semi-insulation film 52 containing ZnO or the like disposed on thephotoelectric conversion layer 51, bonding portions 54 embedded in asurface of the semi-insulation film 52, catalytic metal portions 53disposed on the bonding portions 54, fine catalytic metal particles 55disposed on the semi-insulation film 52, graphenes 56A disposed betweenthe fine catalytic metal particles 55 or between the fine catalyticmetal particle 55 and the catalytic metal portion 53, and graphenes 56Bstacked over the graphenes 56A. In Embodiment 5, the conductive film isused as a transparent electrode. When the patterns of the catalyticmetal portions 53 and the bonding portions 54 are optimized, theresultant transparent electrode can be excellent in current property andlight transmission. In addition, since the graphenes have a highmechanical strength and an excellent bending property, the transparentelectrode can be used in a flexible display or the like.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

1. A semiconductor device comprising: a substrate; an insulation filmdisposed on the substrate; and a conductive film disposed on theinsulation film, wherein the conductive film contains a fine catalyticmetal particle as a junction and a graphene extending in a network formfrom the junction, and the graphene in the conductive film is separatedfrom the insulation film by a gap.
 2. The semiconductor device accordingto claim 1, wherein the fine catalytic metal particle is prepared from ametal film formed on the insulation film by a plasma treatment, and theamount of the fine catalytic metal particle on the insulation film iscontrolled by changing the thickness of the metal film.
 3. Thesemiconductor device according to claim 1, further comprising: a viahole extending through the insulation film; and a further conductivefilm disposed in the via hole, wherein the conductive film disposed onthe insulation film is integrally connected with the further conductivefilm disposed in the via hole.
 4. The semiconductor device according toclaim 1, further comprising: an embedded portion containing a metal orcompound selected from Ti, TiN, and TaN, disposed on a part of theinsulation film; and a catalytic metal portion having a compositionequal to that of the fine catalytic metal particle, wherein thecatalytic metal portion is electrically connected to the conductivefilm.
 5. The semiconductor device according to claim 1, wherein theconductive film is used in a channel region.
 6. The semiconductor deviceaccording to claim 1, wherein the conductive film is used as atransparent electrode.
 7. The semiconductor device according to claim 1,wherein the conductive film has a three-dimensional structure.
 8. Thesemiconductor device according to claim 1, wherein the conductive filmfurther contains a graphene free from the fine catalytic metal particle,stacked over the graphene extending in the network form from thejunction.
 9. The semiconductor device according to claim 1, wherein thefine catalytic metal particle contains at least one selected from Cu,Ni, Co, Fe, Ru, Ti, In, and Pt.